Do you own an iPod?
I keep ZERO music files on my computer; that’s what the Pod is for. I set iTunes for “manual updating” and manage the iPod just as you say: “drag and drop.” I’ve never lost anything.
Oh, well I enabled manual update AFTER putting songs into the iPod and then deleting the files in the computer. I figured what stays in the iPod will continue to do so, after. I was wrong.